1. Field of the Invention
The present invention relates to a process for the forming of a powdered composition of a sulfonated EPDM terpolymer, having less than 1.25 wt. % ENB wherein the powder has a particle size distribution of from about 500 to about 3,000 microns, a water content of less than 2 wt. %, and a sulfonate content of less than 250 meq./100 g polymer.
2. Description of the Prior Art
Recently, a new class of thermoelastic sulfonated polymers has been described in a number of U.S. Patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728, herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The sulfonate groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically cross-linked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically cross-linked elastomers may be processed like conventional thermoplastics at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups IA, IB, IIA, IIB and aluminum, iron, cobalt and lead and mixtures thereof of the Periodic Table of Elements. Although these sulfonated elastomeric polymers prepared by the process of this patent are readily usable in a certain number of limited applications, they are not as readily adaptable for blending with fillers and oil extenders and polyolefinic resins due to their inability to be formed as a powder but rather being produced as large particle size pellets (.gtoreq.1/8").
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the sulfonated elastomeric polymers are organic amines. Again, these compositions were not produced as powders.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. F. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming. The compositions formed by this process are again not powders.
U.S. Pat. No. 3,847,854, herein incorporated by reference, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debyes, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer. Again, the compositions of this invention are not powders.
Products resulting from the aforementioned methods for obtaining neutralized sulfonated elastomeric compositions are not capable of being readily blended with extenders to produce homogeneous dry blends.